San Francisco appears poised to become the first city in the U.S. to require a cell phone makers to publicly display how much radiation their products emit.

On Tuesday, the city's board of supervisors voted 10-1 in favor of a new law that requires handset makers to post in stores their products' specific absorption rate (SAR), which is a measure of the amount of radio waves absorbed by the user's body. (See also: CNET's Quick Guide: Cell phone radiation levels)

San Francisco Mayor Gavin Newsom is expected to sign the measure into law.

There's no scientific consensus on the dangers of cell phone radiation. Scientists know that humans absorb radiation from cell phones, but it's not known if that absorbed radiation causes health risks, such as cancer. Some studies suggest that it does, while others do not. Scientists concur that more data is needed.

That said, the Federal Communications Commission has set exposure limits for radiation. And the agency requires that all phones emit a SAR that is less than 1.6 watts per kilogram.

Some advocates say cell phones should have warning labels on them. But the wireless industry has fought this type of action. The CTIA, the trade association that lobbies in Washington, D.C., on behalf of wireless operators and cell phone manufacturers, said that it's against the San Francisco ordinance.

"Rather than inform, the ordinance will potentially mislead consumers with point-of-sale requirements suggesting that some phones are 'safer' than others, based on radio frequency emissions," John Walls, a spokesman for the CTIA told the San Francisco Chronicle.

While the dangers of using a cell phone are still unknown, groups such as the Environmental Working Group, a private government watchdog group, believe that consumers can take measures to protect against radiation exposure. The group suggests that cell phone users text rather than talk on their cell phones, and that they use a headset or speaker phone to keep the device away from the head. Other suggestions include turning off the cell phone when it's not being used.

About the author

Marguerite Reardon has been a CNET News reporter since 2004, covering cell phone services, broadband, citywide Wi-Fi, the Net neutrality debate, as well as the ongoing consolidation of the phone companies. E-mail Maggie.
See full bio